The following definitions and descriptions are provided to clearly define certain terms used throughout this application. As used herein, these terms are intended to have the meanings set forth below.
1. Primary fiber optic strandxe2x80x94a fiber optic strand that is connected to an electronic device in the central office of a service provider. A primary fiber optic strand supports a single fiber optic electronic device in the central office and up to 32 different fiber optic electronic devices external to the central office, i.e., one fiber optic strand can be split into 32 different strands for connection to 32 different fiber optic electronic devices.
2. Fiber optic cablexe2x80x94a cable that contains a multiple number of fiber optic strands.
3. Distribution splitterxe2x80x94a splitter used in the intermediate portion of a deployment network, where fiber optic strands are separated and directed to different locations. Distribution splitters divide a single fiber optic strand into multiple numbers of strands.
The number of splitters in a network depends on the total number of strands in the fiber optic cable leading into a central office. The total number of strands in the cable is at least equal to the number of fiber optic electronic devices connected at the central office.
For purposes of describing the present invention, it is understood that, although only two levels of splitting are described herein, any number of levels could be used to divide a primary fiber optic strand into multiple strands. In fact, instead of using distribution splitters and local terminals, a single primary fiber optic strand could go directly to a local terminal with a 1xc3x9732 splitter, in which case the local terminal splits the strand into 32 separate strands which may be connected to 32 individual fiber optic drops leading to one or more subscriber premises.
4. Secondary fiber optic strandxe2x80x94the strands that are separated from a primary fiber optic strand. When a primary fiber optic strand goes through a first distribution splitter, the separated strands are referred to as secondary fiber optic strands. The number of secondary fiber optic strands in the network depends upon the configuration of the splitter, e.g., a 1xc3x978 splitter would split a primary fiber optic strand into eight secondary fiber optic strands. Through each set of splitters, the number of fiber optic electronic devices supported becomes progressively smaller until there is only one device per strand.
5. Splice case or splicerxe2x80x94case that attaches to a fiber optic cable and separates one or more fiber optic strands from the cable to be diverted away from the cable in a different direction. A splice case contains fiber optic splices or permanent connections between two fiber optic strands.
6. Local terminalxe2x80x94an outside plant cable terminal used in the prior art for terminating one or more fiber optic strands near one or more subscriber premises for connection to copper wire drops into each subscriber premises. Under the current invention, local terminal comprises a splitter-terminal apparatus that splits a final fiber optic strand into multiple strands each fitted with a connectorized termination for joining one fiber optic drop.
7. Fiber optic dropsxe2x80x94small fiber optic cables that contain one or two fiber optic strands connecting the local terminal to the customer location. The fiber optic drops connect to the individual fiber optic electronic devices at the customer location.
8. Connectorized terminationxe2x80x94a fitting for a fiber optic cable or strand that facilitates quick connections between two different cables or strands. The fittings are typically snap-on plastic connectors with a male and female side, e.g., SC connectors.
9. Pigtailxe2x80x94a short length of jacketed fiber optic strand permanently fixed to a component at one end and a connectorized termination at the other end, such that the pigtail provides a flexible fiber optic connection between the component and the connectorized termination.
1. Field of the Invention
The present invention relates to fiber optic cable systems and, more specifically, to a fiber optic deployment system and apparatus for providing a continuous, uninterrupted fiber optic service from a service provider central office to subscriber premises.
2. Background of the Invention
It is well known in the art that using fiber optic cabling and transmission means in a network provides many advantages over other cabling and transmission systems. Fiber optic systems provide significantly higher bandwidth and greater performance and reliability than standard copper-wired systems. For example, fiber optic systems can transmit up to 10 gigabits per second (Gbps) in comparison to copper lines, which transmit at typically less than 64 kilobits per second (Kbps). Optical fibers also require fewer repeaters over a given distance than copper wire does to keep a signal from deteriorating. Optical fibers are immune to electromagnetic interference (from lightning, nearby electric motors, and similar sources) and to crosstalk from adjoining wires. Additionally, cables of optical fibers can be made smaller and lighter than conventional cables using copper wires or coaxial tubes, yet they can carry much more information, making them useful for transmitting large amounts of data between computers and for carrying bandwidth-intensive television pictures or many simultaneous telephone conversations. However, implementation of complete fiber optic networks from a service provider directly to subscriber premises, e.g., fiber to the home (FTTH), has been very slow due to the high installation cost.
Instead of implementing FTTH networks, service providers have developed strategies to provide some of the benefits of fiber optic networks without actually deploying fiber all the way to the home (or other end-subscriber location). One such strategy is known as fiber to the curb (FTTC) where fiber optics are used between the service provider and local terminals (also referred to as outside plant cable terminals) which are situated in areas having a high concentration of subscribers. The last leg of the network, i.e., from the local terminals into a subscriber premises is made using copper wire drops. Such FTTC systems provide the benefits of fiber optic systems, described above, as far as the fiber extends, but deprives the subscriber of the full benefit of fiber optic networks because of the limiting copper wiring. The only way to gain the full benefit of fiber optic networking is to use a continuous, complete fiber optic connection from the service provider""s equipment to the subscriber""s equipment.
As noted earlier, copper wire drops are used because of the prohibitively high cost of installing fiber optic drops using conventional systems and methods. The bulk of these costs can be attributed mainly to the highly skilled labor and time required to install fiber optic splitters and to join fiber optic drops to fiber optic strands coming from the splitters. In conventional systems and methods, fiber optic networks use fiber optic splitters and splice cases to route fiber optic strands throughout a distribution network. The fiber optic splitters and splice cases allow a fiber optic strand to branch into multiple strands widening the network""s coverage area. In conventional networks, design engineers use splitters and splice cases to route strands from electronic devices at the central office to distribution locations, such as those in housing developments.
From the distribution locations, individual fiber optic drops into each subscriber""s premises must be manually spliced onto each strand. Alternatively, each time a new subscriber requires fiber optic service, one of the fiber optic strands could be manually fitted with a connector for joining a fiber optic drop to the new subscriber""s premises. Thus using the convention systems and methods, installation of individual fiber optic drops to every subscriber""s premises is time-consuming and expensive. As discussed above, to overcome the high installation costs in conventional networks, the fiber optic strands from the distribution locations are run to electronic devices located in local terminals, e.g., aerial or buried terminals, situated in the center of a cluster of subscriber houses. The fiber optic service ends at these electronic devices and copper wire drops complete the connection to the subscriber premises. The copper wire drops are used because no device exists in the prior art that facilitates an economical, easy-to-connect fiber optic drop to the subscriber premises. Although the prior art includes fiber optic splitters and splices for network deployment, the existing splitters and splices are not appropriate for installing individual drops to subscribers because they do not provide a terminating function and they are not combined into an easy to deploy unit.
Further, the conventional fiber optic splitter apparatus present difficulties with ease of connection. The fiber optic splitters known in the prior art are designed to accommodate permanent connections. The splitters are installed at network branch locations at which the number and structure of incoming and outgoing strands rarely change.
The present invention is a fiber optic network deployment system and apparatus for deploying fiber optic strands from a service provider""s central office to individual subscribers"" premises. As shown schematically in FIG. 1a, the invention comprises a central office fiber optic electronic device, a primary fiber optic cable (or strand), distribution splitters, secondary fiber optic cables (or strands), local terminals (outside plant cable terminals), fiber optic drops, and subscriber fiber optic electronic equipment located on subscriber premises. The present invention enables economically feasible deployment of complete, uninterrupted fiber optic services to individual subscribers. The fiber optic deployment system includes local terminals comprising fiber optic splitter-terminal apparatus that enable the cost-effective installation of fiber optic drops to each subscriber.
As shown in FIG. 1a, the system components are connected in a branched network. Starting from the service provider""s central office, a primary fiber optic strand is routed to a distribution splitter that divides the primary fiber optic strand into multiple secondary fiber optic strands, forming a secondary fiber optic cable. As the secondary fiber optic cable extends through the network, secondary fiber optic strands from the cable are spliced off and directed to local terminals within service areas. The local terminals comprise a novel fiber optic splitter-terminal apparatus, described below, to further split the secondary fiber optic strands into individual fiber optic drops routed from these splitter-terminals to the subscriber premises. Once inside the subscriber premises, the fiber optic drops are connected to a subscriber fiber optic electronic device, such as an optical network terminal. The result is complete, uninterrupted fiber optic service from the central office to the subscriber""s electronic equipment which can serve various subscriber electronic devices (e.g., personal computer, television, telephone).
The above-described fiber optic network deployment system can support data, analog video, and voice transmission, with each configuration requiring different equipment at the service provider central office. The preferred embodiment of the deployment system eliminates the use of active components (e.g., remote terminal sites containing multiplexers, host digital terminals, digital loop carrier systems, and other electronic equipment) throughout the distribution network. The only active components are found at the ends of the network, in the service providers"" central office electronic equipment and the electronic equipment located in subscribers"" premises. The resulting passive optical network greatly reduces the probability of trouble reports and decreases the cost of provisioning, maintaining and repairing the system.
FIG. 1b illustrates a fiber optic deployment within a community of subscribers. The primary fiber optic cable from the central office enters the community at three hub locations. At these locations, the primary strands are split and diverted to individual branches. Along the branches, a multiple number of terminals are present. Each terminal location along these branches indicates the number of drops leading to individual fiber optic electronic devices at subscriber locations.
In the present invention, local terminal comprise a specialized splitter-terminal to connect incoming fiber optic strands to fiber optic drops, thereby providing complete, uninterrupted fiber optic service. The splitter-terminal replaces the conventional fiber-to-copper interface and provides a fiber optic connector interface between a fiber optic strand and multiple fiber optic drops to subscriber premises.
A fiber optic network deployment apparatus, also referred to as xe2x80x9csplitter-terminal apparatusxe2x80x9d herein, combines into a single inexpensive apparatus a means for splitting and terminating a fiber optic strand for deployment to a cluster of subscriber premises. The splitter-terminal provides easily accessible, easily connectable terminations from which to run fiber optic drops to subscriber premises. Further, the splitter-terminal apparatus provides strain relief for the delicate fiber optic strands being split or being joined to the fiber optic drops. Finally, as described below, the splitter-terminal apparatus can be modified to accommodate aerial and buried deployment applications.
As shown in FIGS. 2a and 2b, a preferred embodiment of the splitter-terminal includes a splitter, a housing, and a plurality of connectorized terminations which together make up a splitter-terminal package. An incoming fiber optic strand connects to the splitter. The splitter divides the fiber optic strand into a plurality of fiber optic strands extending from the splitter to the connectorized terminations.
The incoming fiber optic strand connects to the splitter through an incoming connectorized termination, e.g., a SC or ST connector. The connectorized termination is attached to the housing of the splitter-terminal package. In another embodiment of the present invention, shown in FIGS. 2c and 2d, the splitter-terminal package includes a pigtail permanently connected to the splitter. In this embodiment, the free end of the pigtail is fitted with a connectorized termination for easily connecting the incoming fiber optic strand. This pigtail extends through the wall of the housing so that the internal splitter-terminal components remain protected by the housing.
Using connectorized terminations allows service providers to field-install the splitter-terminal packages without the need for fiber optic splicing in field. Pigtails are more suited for manufactured assemblies, where an entire splitter-terminal package is delivered to the field.
As illustrated in FIGS. 4a-6c, further embodiments of the present invention use the splitter-terminal package in a larger deployment system, e.g., aerial or buried deployment systems. These larger deployment systems include a splice case and fiber optic drops, in addition to the splitter-terminal package. The splice case connects to a secondary fiber optic cable and separates a secondary fiber optic strand from the bundle. The separated strand becomes the incoming fiber optic strand connected to the incoming side of the splitter-terminal package.
On the outgoing side of the splitter-terminal package, the outgoing connectorized terminations connect to fiber optic drops. Each fiber optic drop proceeds to a subscriber premises for connection to a subscriber fiber optic electronic device such as an optical network terminal. Thus, continuous, uninterrupted fiber optic service is delivered all the way to the subscriber premises serving subscriber electronic devices (e.g., television, telephone, personal computer). This fiber optic network deployment system eliminates the inferior copper drop connections prevalent in the prior art.
The connectorized terminations provide an easy, economical way to connect and disconnect fiber optic drops without the necessity of performing fiber optic cable splicing operations. This advantage affords service providers with greater flexibility in accommodating changes and additions to existing fiber optic networks. For example, connectorized terminations easily accommodate new subscribers, as is often the case in a new housing development. Similarly, in the event that a fiber optic drop to the subscriber is damaged, the service provider can abandon the existing drop and opt for the more cost-effective repair of installing a new fiber optic drop from the fiber optic splitter to the subscriber premises.
Aerial deployment systems arrange the splice case, splitter-terminal package, and fiber optic drops in a variety of configurations. Two examples are pole-mounted systems and strand-mounted systems, shown in FIGS. 4a-4b and 5, respectively. In a pole-mounted system, the splice case is attached to the secondary fiber optic cable, the splitter-terminal package is mounted on the pole, the incoming fiber optic strand runs from the splice case to the splitter-terminal package, and fiber optic drops connected to the outgoing side of the splitter-terminal package run from the pole to the subscriber premises.
In a strand-mounted system, both the splice case and the splitter-terminal package are mounted inside a splice case housing that is lashed with wire to a secondary fiber optic cable. The splice case splices off the incoming fiber optic strand that runs from the splice case to the splitter-terminal. The fiber optic drops connected to the outgoing side of the splitter-terminal package run from the strand-mounted splice case housing directly to the subscriber premises.
Buried deployment systems mount the splitter-terminal package and splice case in a pedestal shell that rests on the ground. As shown in FIG. 6a, a secondary fiber optic cable enters and exits the pedestal shell from the pedestal shell bottom. The splice case connects to the secondary fiber optic cable and splices off an incoming fiber optic strand that runs from the splice case to the splitter-terminal package. The fiber optic drops connected to the outgoing side of the splitter-terminal exit the pedestal through the pedestal shell bottom and proceed underground to the subscriber premises.
As shown in FIG. 6b, in another embodiment of the buried deployment system, the splice case resides underground with a secondary fiber optic cable, as opposed to being contained in the pedestal shell.
In each of the above-described deployment systems, the incoming fiber optic strand running from the splice case to the splitter-terminal package can be connectorized or spliced. The use of either spliced or connectorized terminations for the splice case and incoming side of the splitter-terminal package depends upon the service provider""s intended method of installation. If the service provider desires more factory pre-assembly, the incoming fiber optic strand would be spliced to the splice case and splitter-terminal package at the factory and delivered as a pre-connected unit. If field assembly were desired, service providers would manufacture the splice case and incoming side of the splitter-terminal package with connectorized terminations so that the components could be connected in the field. This would also allow customizing of the length of the incoming fiber optic strand to accommodate field requirements.
Accordingly, it is an object of the present invention to provide a fiber optic network that delivers uninterrupted fiber optic service from a central office to subscriber premises.
It is another object of the present invention to provide an inexpensive apparatus that splits and terminates a fiber optic strand for delivery through fiber optic drops to individual subscribers.
It is another object of the present invention to provide a fiber optic network deployment system that deploys fiber optic strands in a network architecture that maximizes connected subscribers and minimizes the lengths of the strands and the number of active components.